高氮/低氧混合气氛下热处理对氮化铝粉末抗水解性能的研究

研究了在高氮/低氧混合气氛下热处理对氧化铝粉体表面特性及粉体抗水解性能的影响。实验结果表明:经过600℃改性后的AlN粉末表面覆盖了氧化铝薄膜层结构,粉末在水中具有较好的稳定性,有效地抑制了AlN粉末与水的反应,阻碍了水向AlN粉末表面侵蚀的作用,提高AlN粉末在潮湿环境的抗水化能力,且热处理后粉末在水溶液中高剪切应力球磨过程中具有非常好的稳定性。     

磷酸酸洗对AlN粉末抗水解性能的影响

通过测定磷酸酸洗后的亚微米和纳米AlN粉末在水解时pH值随时间的变化,研究了磷酸酸洗和粉末粒度对氮化铝粉末抗水解性能的影响。结果表明,磷酸酸洗能有效提高AlN粉末的抗水解性能,并且酸酸洗效果随粒度的减小而加强。利用XRD和DSC-TGA分析了磷酸酸洗提高AlN粉末的抗水解性能的机制。结果表明,磷酸酸洗无新相生成,酸洗对氮化铝粉末的保护只发生在粉末的表面,并且使表面钝化。     

表面涂覆氮化铝粉末的抗水化性

研究了表面涂覆硬脂酸和吐温80对氮化铝粉末抗水化性能的影响。经过表面改性工艺处理的氮化铝粉末在20～60℃具有很好的化学稳定性,溶液pH值在9.88基本保持不变;改性处理的氮化铝粉末在水中长时间浸泡,X射线衍射分析表明其物相为AlN相。通过表面改性工艺在氮化铝粉末表面包裹一层有机化合物,能有效地抑制氮化铝与水的反应,阻碍水分子向氮化铝粉末表面侵蚀,提高氮化铝粉末在潮湿环境的抗水化能力。     

改性氧化铝粉制备高性能陶瓷浆料的研究

利用油酸对氧化铝粉体进行表面改性,研究了表面改性工艺对氧化铝粉沫表面特性及粉体制备的浆料性能的影响.实验结果表明:改性后粉体表面覆盖由碳氢长链组成的非极性有机表层结构,消除粉体间的硬团聚,制备出固相体积分数达55vol%的氧化铝浆料.     

含C源AlN陶瓷基片烧结工艺研究

采用石墨发热体高温炉,对流延工艺成型的AlN陶瓷基片进行了几种烧结温度、时间的实验,并与金属发热体常压高温烧结炉烧制的AlN陶瓷基片进行了体积密度、硬度、气孔率、表面形貌和晶体结构的对比。实验表明,石墨发热体高温条件下形成的C源,对AlN陶瓷基片烧结影响不大;高温烧结条件下助剂的烧结作用明显,会提升助剂晶相的含量;可以选择性引导AlN晶面的生长;保持低温烧结条件,有利于保持AlN晶相结构。     

不同沉淀剂制备的纳米氧化钛粉体晶相控制

在水解沉淀法制备纳米TiO2粉体的过程中，使用不同的沉淀剂获得了晶相组成(金红石与锐钛矿比例)不同的粉体。使用混合沉淀剂，通过控制沉淀剂的比例，制备出了晶相组成不同的粉体。采用XRD与TG—DTA法检测并探讨了粉体晶相转变的相变温度。实验结果表明：沉淀剂不同晶相转变的温度不同，由非晶态向结晶态转变的相变温度介于225～238℃之间，由锐钛矿向金红石转变的温度介于486～580℃之间，完全转变的温度介于360～817℃之间。分析研究认为，纳米Ti02粉体的晶相组成不仅与沉淀剂种类、混合沉淀剂中各沉淀剂的比例，以及粉体的煅烧温度有关，而且与粉体表面界面相的稳定性有关。     

硅烷偶联剂水解及对钛白粉的改性研究

通过电导率对乙烯基三乙氧基硅烷偶联剂（A-151）的水解行为进行研究,考察了pH、水与A-151体积比和温度对硅烷水解行为的影响,利用A-151的水解特性,对经锆铝二元包覆后的钛白粉进行表面改性,并采用表面接触角测试仪、红外光谱和扫描电镜对有机改性后的二氧化钛进行表征。表面接触角测试显示改性后的二氧化钛制片表面润湿角达108.2°;改性后的粉体在波数为3 078 cm-1处出现了对应的烯烃C-H伸缩振动吸收峰;扫描电镜照片显示改性后的二氧化钛粒子的分散性得到了改善。     

燃烧合成AlN粉体的放电等离子烧结及其导热性能

利用放电等离子烧结(spark plasma sintering,SPS)工艺研究了燃烧合成法制备的2种具有不同形貌的AlN粉以及1种碳热还原氮化法制备的市售亚微米级AlN粉的烧结性能、致密化机理以及导热性能。结果表明:燃烧合成法制备的AlN纳米晶须状粉末具有与亚微米级标准市售AlN粉末同样优异的烧结性能,都能够在无烧结助剂情况下在1600℃的较低温度下烧结致密。在烧结过程中,由于燃烧合成AlN粉自身的高化学活性和SPS产生的等离子体活化作用,使得AlN粉以自身的分解-再结晶-凝聚机制进行致密化,导致晶界强度很高,断裂时以穿晶断裂为主;而在市售AlN粉末烧结过程中以表面扩散机制致密化,在晶界处形成了AlON相,降低了晶界强度,因此以沿晶断裂为主。AlN原料的氧含量对热导率的影响很大。由于燃烧合成AlN粉体的氧含量较碳热还原法制备的市售AlN粉体略高,导致其烧结试样热导率略低。     

二氧化钛粉体的表面改性研究

针对二氧化钛和二氧化硅粉体的表面改性,研究了不同偶联剂种类、偶联剂含量和不同水解环境下粉体的改性效果.实验结果显示,对于不同种类偶联剂KH550、KH560、KH570改性二氧化钛,KH570改性的二氧化钛沉降体积最大,亲油化度也最大,改性效果较好.在中性预水解条件下偶联剂对二氧化钛粉体的改性效果均优于酸性和碱性条件....     

PbO_2粉体的表面改性研究

本文在水溶液中用表面包覆法对PbO2粉体进行有机改性,并通过正交实验法系统地研究了改性过程中主要因素对改性效果的影响,得到最佳改性工艺。实验结果表明,最佳改性工艺为:改性剂比例为3.5%,pH值为5,温度为55℃,改性剂浓度为4mmol·L-1,改性时间为5h。有机改性剂吸附在PbO2粉体表面,在粉体间形成阻隔,减少了粉体间的团聚现象。     

Hydrolysis control of alumina and AlN mixture for aqueous colloidal processing of aluminum oxynitride

AlN powder, surface modified by phosphoric acid treatment was employed for the aqueous colloidal processing of Aluminum Oxynitride (AlON). The hydrolysis of AlN leads to the formation of Al(OH)₃ and NH₃. On mixing of alumina to the phosphoric acid treated AlN in aqueous medium this reaction reoccurred. The phosphoric acid shield around AlN particles is ruptured by alumina addition thus exposing AlN surface to hydrolysis reactions. Hence hydrolysis can be effectively controlled by providing a phosphoric acid treatment to the alumina, prior to its addition to AlN. AlON precursor mixture thus obtained can be successfully shaped by an aqueous slip casting process and sintered to phase pure AlON at 1925 °C for 2 h. Viscosity, pH, SEM, FTIR, and XRD measurements are employed to elucidate the effect of Al₂O₃ addition on surface modified AlN for colloidal processing of AlON.     

Surface treatment and hydrolysis kinetics of organic films coated AlN powder

Abstract

The resistance to hydrolysis of aluminium nitride (AlN) powder was improved by coating the surface of the AlN particles with oleic (OA) and 8-hydroxyquinoline (HQ). The treated powders did not react with water at 40°C when soaked for up to 70 h at constant pH, whereas under the same conditions uncoated AlN reacted with water after 2–10 h soaking. However, with an increase in temperature (65–80°C), hydrolysis of the coated powder took place rapidly. The hydrolysis kinetics of AlN powder with OA and HQ films were found to occur in two stages, a diffusion controlled stage and a surface reaction controlled stage, both of which were first order reactions with activation energies of 125 and 114 kJ mol^-1, respectively. The increased resistance to hydrolysis was the result of the organic films forming a diffusion barrier between the water and the AlN surface. Hydrolysis of the coated AlN powder at high temperature was attributed to the ready breakdown of the film by erosion by the hot water. This explanation was supported by TG–DTA, XRD, and IR examination.     

Hydrolysis Control of AlN Powders for the Aqueous Processing of Spherical AlN Granules

Spherical granules of aluminum nitride (AlN) with an average particle size of about 50 μm were produced from aqueous suspensions using an AlN powder surface treated against hydrolysis with aluminum dihydrogenphosphate [Al(H₂PO₄)₃]. Two different amounts of Al(H₂PO₄)₃ were tested and the effects of surface treatment and aging time were evaluated by various techniques (XRD, TG‐DTA, zeta potential and pH measurements). The treated powder exhibited antihydrolytic property and good dispersing behavior, enabling the preparation of low‐viscosity and high‐concentration aqueous AlN slurries for freeze granulation. The spherical AlN granules were sintered in a boron nitride (BN) powder bed followed by ultrasonic washing of the AlN granulates/BN mixture to remove BN. The sintered spherical AlN granules present excellent crystallinity and high sphericity as observed from SEM micrographs.     

Phosphoric acid treated AlN powder for aqueous processing of net-shape dense AlN and β-SiAlON parts

Abstract

Due to fast hydrolysis of AlN when in contact with water, AlN based ceramics are processed in organic solvents, which are volatile, expensive, harmful to the health and environment. The present work intends to protect AlN powder against hydrolysis in order to enable aqueous processing of AlN based ceramics. A commercial AlN powder was treated in an ethanol solution of H₃PO₄ and Al(H₂PO₄)₃ kept at 80°C for 24 h to protect it from hydrolysis. The dispersing behaviour of the treated AlN powder in water and the ability to consolidate defect free parts of AlN and β-Si₄Al₂O₂N₆ ceramics from aqueous suspensions by slip casting and gelcasting techniques were studied. The consolidated parts were then sintered in a graphite furnace and the sintered bodies exhibited properties [bulk density (BD), apparent porosity (AP), crystalline phase composition and microstructural features] similar to those reported in literature for the same materials processed from organic media.     

Mechanism for the hydrolysis resistance of aluminum nitride powder modified by boric acid

Aluminum nitride (AlN) ceramics are becoming cutting-edge materials for electronic information and communication. However, raw AlN hydrolyzed rapidly, and the high storage costs of this material prevent widespread application. In this study, raw AlN was modified by boric acid (H₃BO₃) at 30 °C to enhance hydrolysis resistance. Transmission electron microscope (TEM), X-ray diffraction (XRD), the magic angle spinning nuclear magnetic resonance (²⁷Al-MAS-NMR and ¹¹B-MAS-NMR), and the fourier transform infrared spectrometer (FTIR) were used to characterize the powder before and after treatment, and the mechanism of hydrolysis resistance was determined. Modification with 0.1 M boric acid did not change the crystal phase of the AlN particles. The modified powder did not hydrolyse at 90% humidity and 70° Celsius. In the presence of boric acid, a network structure of B–O–B linkages ([BO_n], n = 3 or 4) formed that was connected to the AlN core via chemical bonds of B–N–Al and B–O–Al. The protective 6 – 10 nm-thick layer that formed on the surface of the AlN crystal, prevented attack by water molecules and hindered the hydrolysis of aluminium nitride. This study provides an alternative means of preparing anti-hydrolysis AlN powders.     

碳酸化法制备α-Al(OH)3包覆CaCO3复合晶须

A carbonation process was developed to coat Al(OH)₃ on aragonite whisker. Al(OH)₃ coating was obtained in a suspension,which contained 3Cao·Al₂O₃·6H₂O(C₃AH₆)-NaOH prepared by adding Ca(OH)₂ to NaAlO₂ aqueous solution.The CaCO₃ whiskers coated with fine particles of Al(OH)₃ were prepared by blowing CO₂ gas into the suspension.The formed Al(OH)₃ adhered to the CaCO₃ fibers as the substrate.In order to coat α -Al(OH)₃ on aragonite whisker , the pH value of the solution must be higher than 10.5.The formation of C₃AH₆ and complexation of calcium carbonate molecule with C₃A were the domain factors to get single aragonite phase whisker. Micro-analysis demonstrated that the existence of Al(OH)₃ crystal coating on the surface of aragonite-type calcium carbonate whisker.After the coated whiskers were treated strongly in an ultrasonic water bath.Al(OH)₃ still adhered to the CaCO₃ whiskers well.The reaction mechanism was also mentioned in this paper.     

表面包覆Al(OH)3改性石墨的研究

采用异相成核法在天然鳞片石墨水悬浮液中 ,使硫酸铝水解 ,在石墨表面包覆一层Al(OH) 3对石墨进行表面改性处理。介绍了包覆条件对石墨表面改性的影响 ,对改性后的石墨进行了形貌观察、接触角测定、差热 -热重分析。研究结果表明 :在适当的条件下 ,可在石墨表面形成Al(OH) 3包覆层 ,pH值为 4 .0时 ,包覆效果最好 ;包覆后石墨的抗氧化性及对水的润湿性均有所提高     

Suppressed Reactivity of AlN Powder in Water at 5°C

The hydrolysis behavior of AlN powder suspensions (5–25 wt%) at 5°C has been investigated to explore the impact of low temperatures on the hydrolysis behavior. Throughout the 312‐h long experiment, the pH value of the suspensions was below 9, where the hydrolysis remained in the induction period and was eventually suppressed due to the formation of a few‐nanometers‐thick film of amorphous aluminum hydroxide gel around the AlN particles, acting as a passivation layer. Moreover, the aqueous part of the suspension possessed a remarkably high value of dissolved [Al(III)]_aq, being an order of magnitude higher at a given pH value than the aqueous AlCl₃ solution.     

Hydrolysis protection and sintering of aluminum nitride powders with yttria nanofilms

Aluminum nitride (AlN) is a promising material for electronic substrates and heat sinks. However, AlN powders react with water that adversely affects final part properties and necessitates processing in organic solvents, increasing the cost of AlN parts. Small quantities of yttrium oxide (Y₂O₃) are commonly added to AlN particles to enable liquid phase sintering. To mitigate the reaction of AlN particles with water, particle atomic layer deposition (ALD) was used to coat AlN powders with conformal films of Y₂O₃ prior to densification and powder processing. When AlN particles were coated with 6 nm thick films of amorphous Y₂O₃, the hydrolysis reaction was significantly suppressed over 48 h, demonstrating that Y₂O₃ nanofilms on AlN powders act as a barrier coating in an aqueous solution. AlN powders with Y₂O₃ addition by particle ALD sintered to high relative densities (≥90% theoretical) after sintering at 1800°C for 50 min.     

Preparation of aluminum nitride green sheets by aqueous tape casting

Aluminum nitride green sheets were prepared by aqueous tape casting. The characteristics of a treated AlN were studied in aqueous ball-milling media. The oxygen content picked up with the increase of ball-milling time. It was noted that the oxygen content of AlN powder with the dispersant DP270 was lower than that of AlN powder without the dispersant DP270. The isoelectric points of the treated AlN with and without DP270 were, respectively, at pH 3.35 and pH 3.90. The dispersant DP270 not only efficiently dispersed AlN powder in water to form a stable suspension, but also formed a coat onto AlN surface to limit hydrolysis of the AlN powder. The tape casting slurry exhibited a typical shear-thinning behavior. Aqueous AlN green tape had a smooth surface and a narrow pore size distribution. Its relative density was 52.6%. No other crystalline phase was detected by XRD except for AlN and sintering aid yttria in AlN green sheet.